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A SYSTEMATIC INVESTIGATION INTO THE CONCEPTS AND APPLICATIONS OF A FOIL WITH A SPINNING CYLINDER AT ITS LEADING EDGE

Conventional airfoil shapes used as lifting or control surfaces experience a point of ineffectiveness at some moderate angle of incidence to a flow stream, due to the introduction of the concept of boundary layer separation. The application of a spinning cylinder to the leading edge of the foil shape has been experimentally found to counteract the problem of separation and permit higher angles of incidence prior to reaching the "critical angle." The concept of the spinning cylinder as a leading edge is here analyzed from the viewpoint of theories of potential flow and boundary layer separation, then a combined analytic approach is made to the problem using techniques derived from both areas. Specific methods of attack, such as conformal mapping of potential flow and momentum evaluation of the boundary layer thickness, are introducted to simplify analysis. A proposed method of quantitative analysis is then presented and attempted for two foil shapes, and the inherent problems of this approach noted. Finally, applications and limitations of the spinning-cylinder foil are discussed with particular emphasis on the possibility of incorporating the concept in hydrofoil operation to decrease the take-off speed required to become foil-borne.